1. Field of the Invention
The invention relates generally to devices and methods for measuring earth formation properties, wherein the measurements may be made while drilling or while performing a wireline measurement.
2. Background Art
A Logging While Drilling apparatus (LWD) is commonly used in boreholes to perform measurements. A known LWD apparatus may include a combination of measurement devices that allows to obtain a number of different measurements using only one apparatus. It is for example common to use a combination of three measurement devices in an apparatus called triple combo. The known triple combo allows measurements of resistivity, neutron porosity, formation bulk density, formation photoelectric factor and natural gamma-ray to be performed. Alternatively, the combination of measurement devices may possibly be used in other logging configuration such as for example in a wireline logging apparatus.
Due to technical constraints when mounting the three measurement devices in a single LWD apparatus, the triple combo must have a minimum length that generally measures approximately 18 m. The length of the triple combo may be a constraint to access certain environments, e.g. an environment in which the borehole defines a curve.